1. Field of the Invention
The present invention relates to an alignment marker, a display device using the alignment marker, and a fabrication method of the display device. More particularly, the invention relates to an alignment marker used for positional alignment between an optical image separation element, such as a lenticular lens, and a display panel in the fabrication process of a display device that displays different images for respective viewpoints (e.g., an autostereoscopic three-dimensional display device); a display device using the alignment marker; and a fabrication method of the display device.
2. Description of the Related Art
In recent years, the number of Liquid Crystal Display (LCD) devices mounted on small-sized electronic equipment such as projectors, mobile phones, and so on, has been increased rapidly to make good use of their features such as low power consumption, reduced weight, and low profile. On the other hand, value-added products that are produced by adding some values to LCD devices have been developed also. An example of the value-added products is an autostereoscopic three-dimensional display device having a capability of displaying stereoscopic three-dimensional images using an optical element that separates images by dividing incident light for different viewpoints (i.e., an optical image separation element or an optical divider element). With the autostereoscopic three-dimensional display device of this type, a viewer can perceive stereoscopic three-dimensional images with naked eyes without using any dedicated eyeglasses. It is common that a lens (e.g., a lenticular lens, a fly-eye lens, and so on) or a parallax barrier is used as the optical image separation element.
Now, conventionally, the positional alignment methods between a lens and a display panel used in the fabrication process of a display device that displays different images for respective viewpoints (e.g., an autostereoscopic three-dimensional display device) are divided broadly into three types.
The positional alignment method of the first type is a method where markers are respectively formed on the display panel and the lens and then, these markers are matched, thereby aligning the positions of the panel and the lens with each other. An example of this method is disclosed in the Japanese Patent Publication No. 5-188498 published in 1993, which is shown in FIG. 1.
With the positional alignment method of the first type, as shown in FIG. 1, positioning marks 101 are formed at predetermined positions on a display panel 100 and at the same time, positioning marks (not shown) are formed at predetermined positions on the surface of a lens 102 (a lenticular lens in the Publication No. 5-188498). Thereafter, mark images 105 of the positioning marks on the lens 102 and the positioning marks 101 on the display panel 100 are matched with each other, thereby aligning the positions of the panel 100 and the lens 102 with each other using the watching means 104 of a positioning apparatus 103 (see Abstract and FIGS. 1 and 4).
The positional alignment method of the second type is a method where incident light is irradiated to a lens to thereby form a light-collected image and then, the light-collected image thus formed is matched with one of markers formed on a display panel, thereby aligning the positions of the panel and the lens with each other. An example of this method is disclosed in the Japanese Patent Publication No. 10-149110 published in 1998 and another example thereof is disclosed in the Japanese Patent Publication No. 2000-194277 published in 2000. FIG. 2 shows the example of the method of the Publication No. 10-149110, and FIG. 3 shows the example of the method of the Publication No. 2000-194277.
With the positional alignment method of the second type shown in FIG. 2, an alignment marker 151 is provided at a predetermined position on a display panel 150 (a driver substrate in the Publication No. 10-149110). The alignment marker 151, which is located outside of the display region of the panel 150, comprises parallel straight lines arranged at predetermined intervals. Incident light 153 is irradiated to a lens 152 (a cylindrical lens formed on the opposite substrate in the Publication No. 10-149110) to thereby generate a light-collected image 154 on the panel 150 due to the light-collecting characteristic of the lens 152. Then, the light-collected image 154 thus generated is matched with a desired one of the straight lines of the alignment marker 151, thereby aligning the positions of the panel 150 and the lens 152 with each other (see Abstract, FIG. 4, and paragraphs 0020 to 0022).
With the positional alignment method of the second type shown in FIG. 3, an aligning and bonding apparatus 200 with the structure shown in FIG. 3 is used. On the table of the apparatus 200, a microlens substrate 204 and a LCD element 205 are stacked, as shown in FIG. 3. Thereafter, laser light emitted from a laser light source 201 is irradiated to the microlens substrate 204 by way of a half mirror 202 and a mirror 203 and concentrated, thereby forming optical spots on the underlying LCD element 205. Subsequently, while comparing the positions of the optical spots with the predetermined positions on the element 205 using monitoring televisions 207 for displaying the images from microscopes 206, the positions of the optical spots are matched with the predetermined positions on the element 205 (see Abstract, FIG. 1, and paragraphs 0042 to 0047).
The positional alignment method of the third type is a method where the position of a display panel and that of a lens are aligned with each other utilizing the change of state of a specific pattern seen by a viewer, where the pattern is formed outside the display region of the display panel. An example of this method is disclosed in the Japanese Patent Publication No. 11-352441 published in 1999 and another example thereof is disclosed in the Japanese Patent Publication No. 11-15086 published in 1999. FIG. 4 shows the example of the method of the Publication No. 11-352441, and FIG. 7 shows the example of the method of the Publication No. 11-15086.
The positional alignment method of the third type shown in FIG. 4 is used for production of a printing matter 250 comprising main image regions 251 and a rectangular frame-shaped gauge region 252 formed to surround the main image regions 251. A gauge 253 is printed in the gauge region 252. The gauge 253 comprises a pattern formed by straight lines with predetermined widths which are arranged in parallel to each other at predetermined intervals. With this method, printing registration is checked using the gauge 253 printed on a printing paper in the above-described manner.
When printing registration is not matched, the respective lines forming the gauge 253 are not printed apparently apart from each other. Thus, printing is performed even on the portions to be blank existing among the adjacent lines and as a result, the entire gauge 253 is destroyed or collapsed. On the other hand, when printing registration is matched, the respective lines forming the gauge 253 are printed apparently apart from each other and the entire gauge 253 is not destroyed nor collapsed. In this way, printing registration can be checked easily with high accuracy by finding whether the gauge 253 is in the printing state.
Moreover, in the case where the printing matter 250 is seen by way of a sheet-shaped lenticular lens in the step of sticking the lenticular lens onto the printing matter 250. When bonding registration is not matched, moire fringes are generated in the gauge region 252 and therefore, the image of the gauge 253 obtained from a sensor comprises light and shade whose values are deviated from their predetermined ones or whose values are dispersed. When bonding registration is matched, moire fringes are not generated in the gauge region 252 and therefore, the image of the gauge 253 obtained from the sensor comprises a uniform density. In this way, bonding registration can be checked easily by finding which one of the images is seen (see Abstract, FIGS. 1 and 2, and paragraphs 0023 to 0028).
With the positional alignment method of the third type shown in FIG. 7, linear black lines 301 are respectively placed at the specified positions of a synthesized image 300 that comprises a plurality of images having parallax arranged in the respective unit pixels on the same plane. For example, as shown in FIG. 7, the black lines 301 are respectively placed at the left and right end positions of the synthesized image 300, to which the cylindrical lens elements (not shown) forming a lenticular lens are respectively opposed. The black lines 301 are located outside of the display region (or the effective region). Thereafter, positioning is carried out in such a way that one of the black lines 301 is seen in its entirety by way of the lenticular lens (not shown), thereby aligning the position of the lenticular lens and that of the synthesized image 300 with each other (see Abstract, FIGS. 8 and 9, and paragraphs 0022 to 0030).
With the related-art positional alignment method of the first type shown in FIG. 1, the position of the positioning marks 101 on the display panel 100 and that of the alignment marks on the surface of the lens 102 are matched. Therefore, it is necessary to form the alignment marks not only on the display panel 100 but also on the lens 102 with high accuracy. However, to form the alignment marks of this type, the photolithography, printing, stamping or ink-jet technique is generally used. This means that the formation process of the said alignment marks is likely to be affected by the surface irregularities of the base material on which the said markers are to be formed. Accordingly, it is difficult to form desired alignment marks on the surface of the lens 102 with high accuracy.
The alignment marks may be formed on the back of the lens 102. In this case, however, the positioning apparatus 103 needs to have the capability that alignment operation can be performed on both of the surface and back of the lens 102 to cope with the accuracy of the lens 102. This requirement raises the price of the positioning apparatus 103.
Moreover, with the related-art positional alignment method of the first type shown in FIG. 1, not only the high-priced positioning apparatus 103 is necessary due to the above-described reason but also the fabrication cost of the lens 102 is raised due to the requirement of formation of the alignment marks. Accordingly, there is a problem that the fabrication cost of a display device using the display panel 100 is increased.
With the related-art positional alignment method of the second type shown in FIG. 2, the light-collected image 154, which is generated on the display panel 150 by the incident light irradiated to the lens 152, and the alignment marker 151 formed on the display panel 150 are matched with each other, thereby aligning the position of the panel 150 and that of the lens 152. This means that no alignment marker is present on the lens 152. For this reason, an ordinary alignment apparatus is unable to be used and a specially-designed alignment apparatus for this method is necessary. Accordingly, there is a problem that the cost of the alignment apparatus is high.
Moreover, with the related-art positional alignment method of the second type shown in FIG. 2, there is a possibility that the light-collected image 154 generated on the display panel 150 with the lens 152 does not focus on correctly due to dispersion of the thickness of the lens 152, the panel 150 or the adhesion layer, which makes the light-collected image 154 unclear. For this reason, it is essential to make adjustment of the light source for individual display devices. As a result, there is a problem that it takes very long time for the alignment operation and thus, the productivity lowers.
With the related-art positional alignment method of the second type shown in FIG. 3 also, there is a similar problem to the above problem of the method of FIG. 2. Specifically, the laser light emitted from the laser light source 201 is irradiated to the LCD element 205 by way of the microlens substrate 204, thereby forming the optical spots on the element 205. Thereafter, positional alignment is carried out while visually comparing the positions of the optical spots and the predetermined positions on the element 205 with each other. Accordingly, there is a problem that it takes very long time for the alignment operation and thus, the productivity lowers.
With the related-art positional alignment method of the third type shown in FIG. 4, the gauge 253 with a specific pattern is formed in the gauge region 252 which is located outside the display region (i.e., the main image regions 251) of the printing matter 250, and the positional alignment is carried out utilizing the light and shade of the images and the existence and absence of moire fringes. However, this method does not refer to the relative positional deviations along the image separation direction (i.e., the optical dividing direction) of the lenticular lens and the rotational direction thereof. For this reason, there is a problem that it takes very long time for the alignment operation and thus, the productivity lowers.
With the related-art positional alignment method of the third type shown in FIG. 7, the linear black lines 301 are respectively placed at the specified positions of the synthesized image 300 and then, aligning operation is carried out in such a way that one of the black lines 301 is seen in its entirety by way of the lenticular lens. Since this method also does not refer to the relative positional deviations along the image separation direction (i.e., the optical dividing direction) of the lenticular lens, there is a similar problem to that of the positional alignment method of the third type shown in FIG. 4.